You're talking about a different kind of judgment than I am, I think, Ralph. With some overlap probably, but still:

The question you're worried about, "given that Bobnar has the high ground, should his player get +2?" is not the one I'm talking about. Suppose that the game's rule is "if a character has the high ground, the player gets +2, even if that's stupid and unrealistic."

The question at hand is, "as Bobnar's taken position on the ridge of the hill, does he have the high ground?" It's more-or-less a matter of fact in the game's fiction.